The Principality of Gwynedd emerged in fifth century Britain during the arrival of the Anglo-Saxons to Britain. Welsh tradition states that Gwynedd was founded by Picts from Lothian invading the lands of the Brythonic Deceangli, Ordovices, and Gangani. The name Gwynedd itself is said to be an early borrowing from Irish.

From their power base in northwest Wales, the rulers of Gwynedd repeatedly ascended to prominence in Wales and survived Saxon attacks and the construction of Offa's Dyke along the Welsh-English border in the eighth century, Viking raids in the ninth century and widespread power struggles within Wales itself until the eleventh century kingdom of Gruffydd ap Llywelyn was crushed by an Anglo-Saxon invasion led by the Saxon Earl Harold Godwineson in 1063.

The dynasty was restored by Gruffydd ap Cynan and made a slow recovery. In 1216 Llywelyn the Great of Gwynedd proclaimed the Principality of Wales at Aberdyfi. The pprincipality lasted until Edward I invaded Wales. The brothers Llywelyn ap Grufydd ( circa 1223-1282) and Dafydd ap Gruffydd (circa 1238 - 3 1283), who reigned briefly in 1283 following the death of his brother at the hands of the English, were to be the last rulers of an independent Gwynedd. Thereafter the principality was annexed to the English crown.